<!DOCTYPE html>
<html>
<head lang="en">
    <meta charset="UTF-8">
    <title>第55个CSS页面</title>
</head>
<body>
<h4>定义块级格式化上下文的元素</h4>
<div style="margin-text-outline:50px; width: 100px; height: 100px; background-color: green; overflow:hidden;">
    <div style="margin-top: 50px; background-color:gold">
        B
    </div>
</div>

</body>
</html>